In typical clusters of computer systems, each type of communication traffic requires its own dedicated network of communication links, and each link is optimized for its own traffic. Two of the traffic types that differ the most are those used to send messages and data and those used to keep time of day clocks in synchronism. In IBM's zSeries clusters of computers, the message links are called InterSystem Channels (ISCs) and the time of day links are called External Time Reference (ETR) links. Both of these links exist as parallel interconnects, and they both require their own set of optical drivers and receivers and fiber optic cables. Having a dual infrastructure is expensive. What is required is a way to avoid the duplication of communications networks.